Thursday, June 7, 2018

The terahertz (THz) generation in a dual-color field was investigated experimentally by precisely controlling the relative time delay τ and polarization θ of dual-color lasers, where the accompanying third-harmonic generation (THG) is employed to determine τ up to the sub-wavelength accuracy. An anticorrelation of the yields between THz and THG with τ was displayed. Compared with the theoretical simulations, the experimental results reveal that the continuum-continuum transitions of the released electron after single-atom ionization are the dominating mechanism for THz generation, which is opposite to the high-harmonic generation (HHG) based on the recollision mechanism, or the radiation induced by perturbative bound-bound transitions.